combo special skill

yeah if you want to activate new special skill or any other skill that have requirements with same heroes then you will need to get whole new Thor and use it as card well atleast with ragged stormer is like that on attacks skills
Edit:
i remember that i have seen somewhere writen that red heroes when you recrut them it will stay maybe only other red heroes gabriel,uriel,morai because it realy hard to get them and noone would sacrifice red hero for special skill

combo special skill

There\'s a card shop in combo skills tab where you can buy some hero cards with stardust (kinda expensive though): they change after a while, so if you\'re lucky enough to see the thor card, you can buy him. Otherwise, you have to recruit him from CSA shop then transform to card ^^